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    <title>Document</title>
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<body>
    <div class="box">
        <div class="top">
            <ul class="sel">
                <li>第一课</li>
                <li>第二课</li>
                <li>第三课</li>
            </ul>
        </div>

        <div id="content">
            <ul style="display:block">
                <li>wr vvvd</li>
                <li>wrt rtert vvvd</li>
                <li>wr vvvrterterd</li>
                <li>wr v43tvvd</li>
                <li>wr vtertevvd</li>
            </ul>
            <ul>
                <li>1111111111111111wr vvvd</li>
                <li>222222222222wrt rtert vvvd</li>
                <li>33333333333wr vvvrterterd</li>
                <li>w444444444444r v43tvvd</li>
                <li>wr4466666666666666666666 vtertevvd</li>
            </ul>
    
    
            <ul>
                <li>wr 十滴水死哦红豆</li>
                <li>wrt 认为我 vvvd</li>
                <li>绕弯儿无翁人 vvvrterterd</li>
                <li>wr 惹我热无</li>
                <li>wr 我问他问题特特热特太突然</li>
            </ul>
    
        </div>

       
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